Date: Thu, 30 Oct 2014 02:23:33 +0200
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Alex Thorlton <athorlton@sgi.com>
Cc: Andi Kleen <andi@firstfloor.org>, linux-mm@kvack.org,
        Andrew Morton <akpm@linux-foundation.org>, Bob Liu <lliubbo@gmail.com>,
        David Rientjes <rientjes@google.com>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Hugh Dickins <hughd@google.com>, Ingo Molnar <mingo@redhat.com>,
        Kees Cook <keescook@chromium.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Mel Gorman <mgorman@suse.de>, Oleg Nesterov <oleg@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>, Rik van Riel <riel@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vladimir Davydov <vdavydov@parallels.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/4] Convert khugepaged to a task_work function
Message-ID: <20141030002333.GA28052@node.dhcp.inet.fi>
References: <1414032567-109765-1-git-send-email-athorlton@sgi.com>
 <87lho0pf4l.fsf@tassilo.jf.intel.com>
 <20141029215839.GO2979@sgi.com>
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On Wed, Oct 29, 2014 at 04:58:39PM -0500, Alex Thorlton wrote:
> On Tue, Oct 28, 2014 at 05:12:26AM -0700, Andi Kleen wrote:
> > Alex Thorlton <athorlton@sgi.com> writes:
> > 
> > > Last week, while discussing possible fixes for some unexpected/unwanted behavior
> > > from khugepaged (see: https://lkml.org/lkml/2014/10/8/515) several people
> > > mentioned possibly changing changing khugepaged to work as a task_work function
> > > instead of a kernel thread.  This will give us finer grained control over the
> > > page collapse scans, eliminate some unnecessary scans since tasks that are
> > > relatively inactive will not be scanned often, and eliminate the unwanted
> > > behavior described in the email thread I mentioned.
> > 
> > With your change, what would happen in a single threaded case?
> > 
> > Previously one core would scan and another would run the workload.
> > With your change both scanning and running would be on the same
> > core.
> > 
> > Would seem like a step backwards to me.
> 
> I suppose from the single-threaded point of view, it could be.  Maybe we
> could look at this a bit differently.  What if we allow processes to
> choose their collapse mechanism on fork?

Yet another knob nobody uses? Let's just do it right.

-- 
 Kirill A. Shutemov
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